1. Field of the Invention
This invention relates generally to methods and apparatus for sterilizing articles and hazardous biological waste, and for the treatment of various substrates. In particular, the invention provides methods and apparatus for sterilizing articles with a gas plasma generated from a gas mixture of oxidizing and reducing agents. Methods and apparatus are also provided for treating, e.g. stripping, cleaning, plasma treating, etching or depositing a film, various substrates with a plasma having a generally uniform density. In one particular aspect, this invention provides for the sterilization of articles with a gas plasma generated from water vapor.
A variety of sterilization methods have been proposed for sterilizing a wide range of articles such as medical products, surgical instruments, pharmaceutical products, and the like. One common method is by subjecting the articles to a gas such as ethylene oxide or other disinfecting gases. Irradiation procedures have also been proposed for sterilizing articles such as medical products.
One expectation for all sterilizing procedures is that they must effectively kill all organisms without damage to the articles or goods being sterilized. Although some sterilization procedures meet these criteria, including the use of ethylene oxide and other procedures, many sterilizers using such gases suffer from number of serious drawbacks. For example, use of such gases is often too corrosive for the articles being sterilized or their packaging materials. Another drawback is that a toxic residue usually remains on the sterilized articles. In another drawback that affects all traditional methods of sterilization, although the microorganisms are usually destroyed by the plasma, the destroyed microorganisms still physically remain on the articles.
Sterilization gas procedures and irradiation procedures often expose workers and the environment to unacceptable safety standards. Such exposure is becoming increasingly more undesirable, particularly in light of state and federal legislation restricting the use of hazardous materials.
Such restrictions are forcing hospitals and other medical facilities to search for other alternatives. One such alternative is a plasma sterilizer. Plasma sterilizers operate by injecting a gas into a chamber and applying electromagnetic radiation energy to the gas in the chamber which in turn ionizes the body of gas. The ionized gas should be highly reactive and reacts with microorganisms on the surface of the articles to be sterilized. The reactions between the ionized gas and the microorganisms should effectively destroy the microorganisms. Sterilizing plasmas have been generated with a wide variety of gases as set forth generally in U.S. patent application Ser. No. 5,184,046, the disclosure of which is herein incorporated by reference.
One drawback with using such plasma sterilizers is that it is often difficult to ensure that all of the articles in the sterilizer have been completely sterilized. Such a problem arises because of the difficulty in achieving uniform gas dynamics and uniform plasma density when the articles being sterilized are of different sizes or shapes. This problem is compounded by the use of non-cylindrical reaction chambers and differing batch sizes. The non-uniformity of the gas dynamics results in a non-uniform plasma density, which in turn provides a non-uniform plasma treatment and insufficient sterilization.
Another problem experienced in sterilizing articles is the problem of maintaining the sterility of the articles during packaging. Current sterilization techniques, such as plasma sterilization and gas sterilization, generally require. the articles to be sterilized and then subsequently packaged. To maintain sterility during packaging, the articles are packaged in a sterile environment. Such a procedure is inconvenient and expensive.
The treatment of hazardous biological waste is also of interest to the invention. Hazardous biological waste is typically collected at the point of source and is usually consolidated with other hazardous biological waste from other sources and different locations. The handling, transportation, and storage of these materials can be problematic and can require special training, handling and tracking. Furthermore, there is a high risk of accidental contamination associated with the handling and storage of such wastes.
To destroy such wastes, the wastes are usually placed in an incinerator and burned at about 3000 degrees C. The burning of the hazardous biological waste in this manner poses various problems since many of the packaging materials are constructed from plastics and release toxic gases when burned.
The treatment of various substrates, such as semiconductor and microelectronic substrates, has also proved to be difficult and challenging. Traditionally, such substrates were processed using wet chemistries. Since the substrates were relatively small and the line geometries were relatively large, non-uniformity of the chemical treatment was not generally problematic. With the demand for larger sized substrates, most manufacturers have resorted to the use of gas plasma processes. However, due to the relatively large size of the substrates, e.g. 400 mm by 400 mm or larger, such processes have proved to be generally ineffective. For example, the achievement of uniform gas dynamics and uniform plasma density within relatively large reaction chambers has been difficult, if not impossible. As a result, both substrate sizes and batch sizes have remained small. Further, such processes have generally produced low yields.
It would therefore be desirable to provide methods and apparatus to overcome or reduce such problems relating to plasma sterilization, the treatment of hazardous biological waste, and the treatment of various substrates. In particular, the methods and apparatus should provide for plasma sterilization that is not corrosive to the articles and does not leave toxic residues on the articles. The methods and apparatus should not only be able to effectively destroy the microorganisms, but also to remove them from the articles. Further, the methods and apparatus should provide for uniform plasma distribution, thereby insuring uniform sterilization regardless of the chamber geometry or the size and geometry of the articles to be sterilized. It would further be desirable to provide methods and apparatus for sterilizing articles within packaging suitable for delivery to an end user.
In the case of biological wastes, it would be desirable to treat the hazardous waste at the production site so that no special handling, transportation or storage of the waste will be required.
In another aspect, it would be desirable to provide methods and apparatus for treating various substrates, regardless of their size. Such methods and apparatus should also allow for large substrate sizes and/or batch sizes, produce good yields, and be economical.
2. Description of the Background Art
U.S. Pat. Nos. 5,115,166, 5,184,046, and 5,325,020 describe various apparatus and methods for plasma sterilization.
U.S. Pat. No. 4,207,286 describes a sterilization method using a continuous flow, low pressure gas plasma.